1. Field of the Invention
This invention relates to pipeline inspection tools, and more particularly to apparatus and methods for determining whether a defect resides on the interior or exterior surface of a pipeline.
2. Background of the Invention
Oil, petroleum products, natural gas, hazardous liquids, and the like are often transported using pipelines. The majority of these pipelines are constructed from steel pipe. Once installed, a pipeline will inevitably corrode or otherwise degrade. Proper pipeline management requires identification, monitoring, and repair of defects and vulnerabilities of the pipeline. For example, information collected about the condition of a pipeline may be used to determine safe operating pressures, facilitate repair, schedule replacement, and the like.
Typical defects of a pipeline may include corrosion, gouges, dents, and the like. Corrosion may cause pitting or general wall loss, thereby lowering the maximum operating pressure of the pipeline. Vulnerabilities may also include curvature and bending anomalies, which may lead to buckling, and combined stress and chemical or biological action such as stress corrosion cracking. Without detection and preemptive action, all such defects and vulnerabilities may lead to pipeline failure.
Information on the condition of a pipeline is often collected using an in-line inspection tool. An in-line inspection tool typically uses sensors to collect information about a pipeline as it travels therethrough. In the past, in-line inspection tools have used magnetic flux leakage to determine the condition of a pipeline wall. Flaws in ferromagnetic pipe can be detected by the perturbations they cause in a magnetic field applied to the wall of a pipeline.
Some in-line inspection tools include primary sensors suitable to identify defects that occur in ferromagnetic pipe both on the inner diameter (ID) or interior surface and on the outer diameter (OD) or exterior surface of the pipe. However, the primary sensors may be unable to determine which are interior defects (i.e., located on the inner diameter) and which are exterior defects (i.e., located on the outer diameter). Accordingly, some in-line inspection tools include secondary sensors tasked with discriminating between interior and exterior defects.
Current technologies require numerous secondary sensors, usually about half the number of primary sensors. Accordingly, current systems are hampered by the cost, power consumption, space consumption, data storage consumption of all those secondary sensors. Thus, what is needed is a new apparatus and method for reducing the number of secondary sensors without reducing the ability to discriminate between interior and exterior defects.